Configure dual hotends in Marlin: https://e3d-online.dozuki.com/Guide/Chimera+Marlin+Configuration/31?lang=en
Dual extruder configuration: http://www.instructables.com/id/TEVO-Tornado-Dual-Extrusion-Beaus-TL-Feeder-Versio/
Marlin GCode commands: http://marlinfw.org/meta/gcode/
Marlin configuration: http://marlinfw.org/docs/configuration/configuration.html
Printing thin walls and small details: https://www.simplify3d.com/support/articles/printing-thin-walls-and-small-features/
3D printing troubleshooting: https://www.simplify3d.com/support/print-quality-troubleshooting/
3D printing guide: https://all3dp.com/3d-printing-3d-printer-guide-101-questions/
Marlin filament sensor: https://github.com/arunoda/marlin/commit/63e770961e0191b32acb55a5225525708706ebec